Recently, semiconductor devices have seen an increase in processing speed by using a fine process as well as analog circuitry, such as a sensor circuit. Especially in a case that an absolutely accurate resistance element is required, the fact that a variation in the amount of analog data output from a circuit varies depending upon the characteristic variation among the transistors is a problem. The variation amount of analog data can be corrected to a predetermined resistance value by disconnecting a fuse made from a poly-silicon or a metal interconnection, or in other words “trimming.” In addition, the trimming serves as a redundancy for defective parts of a DRAM.
A poly-silicon fuse has a disconnection process that includes a simultaneous liquification and vaporization of the poly-silicon fuse by laser exposure. However a metal fuse made from, for example an aluminum, has a disconnection process wherein the vaporization occurs after the liquification. The metal fuse remains in a liquid state longer than a poly-silicon fuse remains in a liquid state. Therefore, in the case of a metal fuse, the liquefied metal can scatter when it is in the liquid state. If the scattered metal attaches to a side of an aperture formed by the laser exposure, there may be caused a defect, such as an incomplete disconnection. An example of this is shown in FIG. 4.
FIG. 4 shows a photograph of a top view of a prior metal fuse after the laser exposure. The photograph is taken with a scanning type electric microscope. An opening 103 is formed in metal fuse 101 by the laser exposure at an insulation layer on the metal fuse 101. As can be seen in FIG. 4, there is a portion of the metal fuse 101 which is not disconnected, “non-disconnection part” 105, at the right side of the opening 103. In addition, scattered liquefied metal can be seen on both sides of the opening 103.
Furthermore, the metal fuse is configured as a metal interconnection layer. For example, a metal layer made from AlCu is formed on a barrier metal layer formed of Ti/TiN stacked sequentially from a bottom layer. Additionally, Ti/TiN layers, such as a cap-metal, are stacked sequentially on the metal layer. In a case where the metal fuse includes the barrier metal, the non-disconnection parts occur on an edge side of the barrier metal, when the metal fuse is disconnected by the laser exposure. As a result of this, the metal fuse is not completely disconnected.
An example of a prior fuse structure is discussed in Japanese Laid-Open Patent Publication No. 2000-286341 (Patent document 1). In Patent document 1, a fuse structure configured as a first metal interconnection layer and a second metal interconnection layer, where the second metal interconnection layer is located above the first metal interconnection and connected to the first metal interconnection through vias. In the Patent document 1, when there is a plurality of fuses, the vias are located alternately. As a result of this, a fuse pitch is shortened.
In addition, another example of a prior fuse structure is discussed in Japanese Laid-Open Publication No. H05-74947. In Patent document 2, an anti-fuse is configured as an electric conductive region located on a semiconductor board and vias located on the electric conductive region through a high dielectric layer. The anti-fuse, which functions conversely to the usual disconnection fuse, is not electrically conductive until the high dielectric layer is provided with a pulse voltage, at which time the condition of the high dielectric layer changes. As a result of this, the high dielectric layer becomes conductive since the resistance value of the high dielectric layer decreases.